String Theory, Membranes, and the Big Bang

[Blueshift5]

Ok, so i have been reading some things presented by Brian Green, and he talks about membranes which are related to the string theory. According the Green, these membranes are actually like universes. When two of them bump into eachother, it creates what we call a big bang in one of them. It would be great if someone could describe how this theory relates to string theory and how realistic this theory really is. Thanks!

[meteor]

and how realistic this theory really is...
How realistic is can be checked by observations. Ok, you have the Cyclic model, in which there are two branes colliding cyclically. One of the assumptions of the Cyclic model is that the density perturbations that will produce the large scale structure observed nowadays are produced before the collision between the branes, that is before what we can call the Big Bang. If you prefere the Standard Inflationary scenario, the density perturbations are produced after the Big Bang. Is possible to detect if the density perturbations were created after or before the Big Bang by searching for tensor fluctuations, non-gaussianity and non-adiabaticity